Electronic equipment which is state dependent and which derives electrical power from line voltage provided by utility companies over a distribution grid is fundamentally vulnerable to system damage and data loss through the loss of continuity of power. This is not a new problem and solutions in the form of uninterruptible power supplies that stabilize the line power reaching sensitive equipment have been available for many years. These devices fall into two categories: the standby power supply and the true uninterruptible power; supply. Each of these categories of device addresses the same problem, and in the vernacular both have come to be known as an uninterruptible power supply (UPS). A commonality of these two forms is that both take power from the AC line, and both output power functionally equivalent to that of the AC line.
In the standby power supply, AC line power is shunted directly to the output so long as good line power is present. Then, in response to sensing the absence of good AC line power, the UPS manufactures stand-by power from a battery bank and feeds it to the output. The true uninterruptible power supply has a central DC bus which is supplied by both battery power and/or rectified AC line current when present. Power from the central DC bus is continuously being inverted and supplied to the output of the UPS. The greater stability of the output due to complete independence from fluctuations of line voltage, together with the elimination of line power quality sensing circuitry make the true uninterruptible power supply a more dependable form of UPS backup than the standby power supply.
Desktop and small computer systems today all have integrated DC power supplies built into them. These supplies are designed to accept AC line voltage and convert it into various line-isolated, DC outputs required by the computer hardware. Today, small computer systems and the UPS's that are often used to provide stability of operation are generally separate components or entities. That is, line power from the mains is fed through a physically and electronically separate UPS, whether a standby power supply or a true uninterruptible power supply. The UPS receives AC input, and provides AC output, often with an intermediate stage in which the power is converted to a DC voltage. This AC output of the UPS is then fed into the normal AC input of the computer system. This arrangement has many inefficiencies, most notably in that the UPS must have separate power supply electronics which often mimic those already present in the computer power supply.
External UPS's have a number of disadvantages in their use. For example, these systems are inherently expensive in the use of redundant parts (electronics, connectors and enclosures). The additional number of power conversions also involve additional power losses. Furthermore, these external UPS systems require the use of additional desktop or floor space, along with the need for additional power cables to connect them to the computer.
Finally, it is of benefit for the computer to have knowledge about the loss of mains power, so that steps may be taken to safeguard information on the computer from eventual loss when the battery supply in the UPS is exhausted. Without some form of explicit communication about the loss of mains power, the computer receiving power from the UPS is not alerted to the potential for eventual loss of power due to battery exhaustion. In order to compensate for this shortcoming, external UPS's often have serial communications capabilities, which are connected through an external serial port on the computer system. However, since many computer systems are delivered with only one or possibly two external serial ports, this communications link between the computer and the UPS consumes a scarce resource.
A UPS internal to the computer would be of general usefulness, but previous attempts have run into a number of technological barriers. For example, computer enclosures are often compact, and the large batteries of most UPS's would not easily fit within their confines. Furthermore, if the UPS is internal to the computer but external to the computer power supply, power from the UPS must be fed back to the power supply so as to reintegrate with normal computer electronics. In addition, the internal UPS is at a disadvantage because the batteries of the UPS must be either accessible for exchange when the batteries exceed their operational life (especially with lead-acid batteries, which have limited lifetimes), or when the computer is disposed of, because of the toxic materials used in many batteries. Another limiting characteristic of an internal UPS is that its batteries are generally not "hot swappable," meaning that the batteries cannot be replaced without the need to power-down the computer. This capability is of particular interest to server computers, which due to their use by a large number of users, must be maintained in the operational state.
In order to address these problems with internal UPS's, attempts have been made to integrate a UPS into computer power supplies. In such an arrangement, mechanical or electrical components of the power supply may be used for the UPS, and the UPS can easily output power into the normal power output of the power supply.
U.S. Pat. No. 5,289,045 to Lavin et al. and U.S. Pat. No. 4,860,185 to Brewer et al. are among prior art methods of incorporating UPS functions into computer power supplies. These patents teach devices in which the UPS circuitry connects directly into the AC-DC conversion electronics of the computer power supply. These devices, however, have numerous disadvantages, such as extensive required modifications of computer power supply circuitry. Furthermore, these devices are not true uninterruptible power supplies, but are switched into the power circuit when a fault is detected. In addition, only minimal power is made available to recharge the UPS batteries after discharge, leaving a time window during which the computer system is vulnerable to subsequent power outages.
It was our intention to create a true uninterruptible power supply that can fit within existing computer power supplies, and which is inexpensive to manufacture, provides sufficient computer system operational time under UPS power so that important data can be safely stored, and which has other features widely desired by users of UPS systems and which are not currently available. It was our intention to solve the problems of the prior art that gave rise to the current invention.